Conclusion

The visibility of interference pattern was 0.495 ± 0.036 for double slits experiment, 0 for both which-path experiment and quantum eraser experiment.

The quantum maker reduced the visibility of interference by 100%, but the quantum eraser restored the visibility by 0%.

The visibility of double slit interference showed the existence of spatial incoherence. The spatial coherence could be improved by extending the length of our experimental black box, so the light source could be approximated as a point source.

The result with the quantum eraser was too noisy. There was no observable restoration of the interference pattern after the quantum eraser was applied. Besides, as we adjusted the polarization of the quantum eraser, the overall number of photon events changes, as if we detected the diffraction of linearly polarized waves. One possible explanation is that the light from one slit is blocked and our result for the second step was in fact a single-slit diffraction. If this holds, then either the marker films overlapped or one film polarizer blocked the light. Both situations are unlikely: we made sure there was no overlapping of the two polarizers.

We recommend future groups redesign the experiment with new apparatus, in attempt to tape the quantum marker right on the slits. It is also recommended that future groups design a new method to mark and erase the information of the photons' choices of paths.

Reference

[1] Aharonov, Yakir; Zubairy, M. Suhail (2005). “Some Light Quantum Mechanics” Science.

https://www.youtube.com/watch?v=MzRCDLre1b4

[2] Hecht, Eugene (2002). “Optics, 4^th Edition”

[3] Chiou, Yang Tan; Xin, Zhi Tan (2017) “Young’s Double-slit Experiment with Single Photons and a Quantum Eraser”